Explosives are used in a significant number of commercial blasting operations, such as mining, quarrying and seismic exploration. In mining and quarrying a detonator is typically used to initiate a cartridged primer charge that in turn detonates bulk explosive. In seismic exploration a relatively small cartridged explosive charge is initiated using a detonator and the shock waves that are generated are monitored and analysed.
When an explosive charge fails to detonate as intended there are obvious safety and security issues. In that event, it may be possible to recover the charge, although this is not always possible for a variety of reasons. For example, in mining applications and seismic exploration where charges or trains of charges are positioned and detonated, recovery of undetonated charges can be difficult, especially when the charge(s) is/are positioned in an underground borehole and the borehole has been backfilled, as is common practice. There are therefore instances where undetonated charges remain unrecovered in the field. In such cases, and as a general point, it would therefore be desirable to render safe any undetonated and unrecovered explosive charges. A variety of approaches to address this need already exist.
By way of example, U.S. Pat. No. 3,948,177, describes an explosive cartridge for underwater blasting which is said to be self-disarming in the event of an underwater misfire. The cartridge comprises a closed shell including an internal conduit. Water external to the cartridge is prevented from flowing into the conduit by a watertight seal. The force of a percussion impact initiation can however break the watertight seal thereby allowing water to flow into the conduit and contact with explosive composition contained. In turn, water can dissolve the (nitrocarbonate) explosive possibly also causing it to flow out of the body of the cartridge. The result is desensitisation. Whilst generally useful, a problem with this approach is that desensitisation is contingent upon some form of specific force associated with a misfire to break the watertight seal. If there is no applied force resulting from a misfire, the cartridge would not be disarmed by the action of water.
Other approaches, such as those described in WO 97/19253 and WO 98/55822, rely on the use of micro-organisms to effect bio-remediation of an explosive composition in the event that the composition is not detonated as intended. According to these disclosures suitable micro-organisms are included within an explosive composition contained in an explosive device. In other words the micro-organisms are intrinsic to the device. However, such approaches are not without practical complexities. Being biological in nature, care needs to be taken to provide the micro-organisms in a form that is active or that has potential to be active, and care needs to be taken not to destroy the micro-organism thereby rendering them useless. It will also be necessary to supply the micro-organisms with suitable nutrients/metabolites in order to sustain them when they are required to be active. Approaches using micro-organisms contained by design within explosive devices may also lead to unwanted introduction or leakage of possibly exotic micro-organisms and/or chemicals into the environment. Thus, the use of micro-organisms in this context is not without problems.
The present invention seeks to provide an alternative approach to rendering safe explosive compositions that does not suffer the disadvantages described above.